1. Field of the Invention
The present invention relates generally to the field of oil and gas, and more specifically, to a method and system for generating hydrogen-enriched fuel gas for emissions reduction and carbon dioxide for sequestration.
2. Description of the Related Art
Climate change resulting in global warming from increased greenhouse gas (GHG) concentration in the atmosphere has been a problem for many years, and the recent accelerated increase in GHG concentration in the atmosphere and the associated climatic impacts identified around the work has been alarming. The anthropogenic (man-made) causes of global warming include carbon dioxide emissions into the atmosphere from hydrocarbon fuel combustion, including, but not limited to, electrical power generation facilities, vehicles, railroad locomotives, ships, airplanes, petrochemical, manufacturing, industrial and commercial industries; methane derived from agricultural sources (e.g., rice paddies, bovine flatulence, etc.), biomass (human waste, animal waste, and agricultural waste), and hydrocarbon fuel production; increased water vapor in the atmosphere from hydrocarbon fuel combustion; nitrous oxide from hydrocarbon fuel combustion; and deforestation, which releases hundreds of millions of tons of carbon dioxide into the atmosphere each year. [1] According to the United Nations Intergovernmental Panel on Climate Change (IPCC), it is projected that global warming will cause dry areas to get drier, drought-affected areas to become larger, an increase in heavy precipitation events, and a decrease in water supply stored in glaciers and snow pack. In addition, coastal areas will be exposed to coastal erosion and sea-level rise, and many millions more people will be flooded every year due to sea-level rise by the 2080s. [2]
Hydrocarbon fuel combustion emissions are a major contributor to GHG concentrations that impact climate change and result in global warming. It has been documented that hydrogen-enriched fuel decreases emissions. [3, 4] The problem that has not been solved, however, is how to produce and develop a hydrogen-based infrastructure. Most of the debate surrounding this issue involves developing a pure hydrogen product that eliminates carbon dioxide emissions from combustion of the fuel. Developing a blended hydrogen and pipeline quality natural gas product that utilizes the existing pipeline transportation and distribution system would reduce emissions from industrial, commercial, residential and mobile natural gas consumers. This problem presents challenges that heretofore have not been solved by the prior art. The present invention offers a solution to this problem by providing a method and system: converting the hydrocarbon molecules to hydrogen and carbon dioxide; separating the hydrogen and carbon dioxide; storing, sequestering or utilizing the carbon dioxide so that it is not emitted into the atmosphere; and blending the hydrogen back into the natural gas and/or using the hydrogen as fuel. In a preferred embodiment, a carbon dioxide recovery solvent is used to separate the carbon dioxide from the hydrogen, which has the advantage of allowing the separation step to deliver the hydrogen and carbon dioxide at high pressure, thereby reducing the cost and energy usage of compressing and transporting carbon dioxide downstream systems and the hydrogen back to the natural gas pipeline. The carbon dioxide recovery solvent also significantly lowers circulation rates when compared to conventional physical and chemical solvents, thereby reducing the energy required and size of equipment needed to implement the process.
The term “carbon sequestration” generally refers to the long-term storage of carbon in a multitude of means, including, but not limited to, terrestrial, underground, or ocean environments to reduce the buildup of carbon dioxide in the atmosphere. [5] One method of containing carbon dioxide—called “geologic sequestration”—is to inject it into geologic formations (e.g., coal beds, petroleum formations, saline aquifers, basalt formations, etc.). Enhanced oil recovery (EOR), a form of geologic sequestration, is the process by which carbon dioxide and sometimes water are injected into oil reservoirs, thereby flushing out reserves of oil that would otherwise remain unrecovered. This process can extend the life of an oil reservoir by years, and in some cases, produce many millions of barrels of extra oil without causing substantial additional impacts to the surface and eliminating or delaying the expansion of oil exploration into sensitive areas. [6] In a preferred embodiment of the present invention, the carbon dioxide that is recovered as part of the present invention is used in EOR operations.
Current technologies for capturing carbon from fossil fuels generally fall into two categories: pre-combustion and post-combustion. To date, pre-combustion technologies have been limited to removal of carbon dioxide from coals, natural gas or syngas immediately prior to combustion. Though many plants have been proposed to deliver the captured carbon dioxide for eventual sequestration, no commercial plants have been constructed to date. Prior art post-combustion technologies are limited to removing carbon dioxide from low-pressure (near atmospheric) flue gases using chemical amine-based solvents or chilled ammonium bicarbonate solvent. These applications typically require high solvent circulation rates, high thermal energy requirements, and often have problems caused by oxygen contamination and high flue gas temperatures. In addition, the delivery pressure of the carbon dioxide from said prior art systems is limited to 5-10 psig (pound-force per square inch gauge), which requires high energy consumption due to compressing the carbon dioxide for sequestration in geological storage reservoirs or for use for carbon dioxide EOR.
Furthermore, much of the prior art deals with carbon capture and sequestration at point sources (e.g., individual stationary facilities); however, most point sources generate relatively small amounts of carbon dioxide that are not of sufficient quantities to support EOR and other types of geologic sequestration. To overcome this limitation, carbon dioxide compression and pipeline networks need to be constructed to aggregate carbon dioxide volumes from point sources, which is only practical for large industrial point sources. The present invention avoids this problem by generating carbon dioxide not at a point source but at a strategically located hydrogen generation plant on the main pipeline (well upstream of the point sources), preferably located in an area that would both geologically support either carbon dioxide storage/sequestration or carbon dioxide EOR injection. In this manner, sufficient quantities of carbon dioxide can be produced to make carbon capture and storage/sequestration economically feasible.